Ecology of the collapse of Rapa Nui society.

Collapses of food producer societies are recurrent events in prehistory and have triggered a growing concern for identifying the underlying causes of convergences/divergences across cultures around the world. One of the most studied and used as a paradigmatic case is the population collapse of the Rapa Nui society. Here, we test different hypotheses about it by developing explicit population dynamic models that integrate feedbacks between climatic, demographic and ecological factors that underpinned the socio-cultural trajectory of these people. We evaluate our model outputs against a reconstruction of past population size based on archaeological radiocarbon dates from the island. The resulting estimated demographic declines of the Rapa Nui people are linked to the long-term effects of climate change on the island's carrying capacity and, in turn, on the 'per-capita food supply'.

Widespread infection of Areospora rohanae in southern king crab (Lithodes santolla) populations across south Chilean Patagonia.

Cottage cheese disease is caused by microsporidian parasites that infect a wide range of animal populations. Despite its potential to affect economically important activities, the spatial patterns of prevalence of this disease are still not well understood. Here, we analyse the occurrence of the microsporidian Areospora rohanae in populations of the king crab Lithodes santolla over ca 800 km of the southeastern Pacific shore. In winter 2011, conical pots were deployed between 50 and 200 m depth to capture crabs of a wide range of sizes. The infection was widely distributed along the region, with a mean prevalence of 16%, and no significant association between prevalence and geographical location was detected. Males, females and ovigerous females showed similar prevalence values of 16.5 (13-18.9), 15 (9.2-15) and 16.7% (10-19%), respectively. These patterns of prevalence were consistent across crab body sizes, despite the ontogenetic and sex-dependent variations in feeding behaviour and bathymetric migrations previously reported for king crabs. This study provided the first report of the geographical distribution of A. rohanae infecting southern king crabs.